1. Field of the Invention
The present invention relates to a push to talk (PTT) system. The present invention in particular relates to techniques of displaying, on each mobile phone in a PTT call, information about the other participant(s).
2. Related Art
Currently, mobile phones which have a PTT function based on VOIP (Voice over Internet Protocol) are widely used in North America.
PTT is explained briefly below.
To initiate a PTT call from a PTT-capable mobile phone, first the mobile phone logs in to a server which mediates PTT calls. The mobile phone then designates another PTT-capable mobile phone as a called party, by ID information used for PTT (hereafter “PTT call ID”).
If the mobile phone designated by the PTT call ID has already logged in to the server, that is, if the designated mobile phone is in an answerable state, a user of the mobile phone can transmit voice communication to the designated mobile phone by pushing a PTT button provided on the mobile phone. Also, by releasing the PTT button, the user can receive voice communication from the designated mobile phone.
A PTT-capable mobile phone stores a PTT directory. The PTT directory is a database for recording and browsing information about contacts (such information is hereafter referred to as “contact information”). A contact mentioned here is a user of another PTT-capable mobile phone who has been established in the PTT directory by a user of the mobile phone.
Contact names showing names of the contacts and PTT call IDs of mobile phones of the contacts can be recorded in the PTT directory as the contact information. Such contact information is displayed on the mobile phone when the user of the mobile phone browses the PTT directory, receives an incoming PTT call, or engages in a PTT conversation.
Conventionally, contact information that can be recorded in a PTT directory is limited to character information. This being so, even if the user views the contact information displayed on the mobile phone when browsing the PTT directory, receiving an incoming PTT call, or engaging in a PTT conversation, he or she may not be able to easily identify a contact represented by the contact information.
Suppose a contact name “Sato” is displayed on a called party's mobile phone as contact information of a calling party upon reception of an incoming PTT call. If the called party knows more than one person whose name is Sato, it is difficult for the called party to identify which Sato is calling.